I saw more and more of this kind of thing last year - girls who don't have the classic 'model' body opting for skimpier styles.
I actually think these look better than full coverage bikinis would on the same bodies - what do other people think? Guys, do you think they look good, girls, do you like them, and would you ever wear them?
I think it's a good thing that people are getting more relaxed about this kind of thing, and also that fewer and fewer people seem to be standing in judgement about it (although I can see that these kinds of people do still exist, from some of the comments you've had).
Lots of people wear them because they don't want the tanlines. There's nothing immoral about it - weird that somebody would even suggest that there is, in 2016...
There a line between being too covered up and having everything hanging out. All the women above look pretty because they seem confident about their body. Though, it doesn't mean it's alright to show your ass in public. They could still go for a flattering bikini that isn't so revealing and look awesome, provided that they feel confident.
I don't really go to the beach, nor do I dress up in swimwear very often... but no, I wouldn't wear something like that. I don't think it looks good. I also have a flat ass so I just prefer wearing shorts over whatever swimwear I have on.
Some of these girls need to cover up their butts; it is definitely not their best ASSet. Actually, seeing one of these butts in bed naked might be fine but they shouldn't have them on display to the public. They really don't look that good. (However, I am not a fan of big butts and those who are may have a different opinion on this subject.)
I haven't been to the beach for a couple of years but you could always see them in southern Europe... not what most people wear but also far from being uncommon. maybe it has gotten more by now but I don't think it will be the standard anytime soon.